Patent Grant
11902750
The present disclosure relates to amplified listening devices, such as hearing aids, personal sound amplification products, and hearing protection devices. More specifically, the present disclosure relates to a system and method that provides an arrangement of two first-order directional microphones arranged in tandem to form a second-order directional microphone system of an amplified listening device.
Hearing aids and similar devices, such as personal sound amplification products and hearing protection devices, have moved closer in form factor and capability to modern wearable devices.
A first-order directional microphone has at most a theoretical 6.0 dB improvement of the desired frontal signal compared to the summed diffuse noise found in loud social gatherings and loud restaurants. In practice, 1-3 dB effective improvement is more common in actual on-head usage.
In contrast, a second-order microphone allows a theoretical 9.5 dB improvement, which under some circumstances may increase the intelligibility of sentences from 35% to 90% correct as measured by accepted tests of hearing ability in noise. Existing approaches to providing a second-order microphone include additional circuitry configured to electronically subtract two first-order microphones (one in front of the other) to form a second-order directional performance microphone.
Moreover, most recent digital first-order directional hearing aids form their directional performance by connecting one omnidirectional (“front”) micro-electro-mechanical system (MEMS) microphone to a first of two analog electrical input and another (“rear”) MEMS microphone to the second inlet, and adding a digital delay to the rear microphone before summing with the front microphone. It is self-evident that with this approach not two but four analog inputs would be required to form a second-order microphone, more than is typically provided by hearing aid circuits. Even if two cardioid electret microphones are connected to the two typically available analog inputs and subtracted to form a second order microphone, in order to provide for an omnidirectional microphone option, which is usually preferred in quiet surroundings, a third microphone input would still be required.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present disclosure as set forth in the remainder of the present application.
Certain embodiments of the present technology provide a system and method for arranging two first-order directional microphones in tandem to form a second-order directional microphone system of an amplified listening device, substantially as shown in and/or described in connection with at least one of the figures.
These and other advantages, aspects and novel features of the present disclosure, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.
Embodiments of the present technology provide a system and method for arranging two first-order directional microphones in tandem to form a second-order directional microphone system of an amplified listening device. Various embodiments provide the technical effect of eliminating additional electronic subtraction circuitry by adding the output of two directional microphones, one of which is modified to produce a reversed phase by using a first directional microphone arranged normally in front and a second directional microphone reversed in space behind, such that a former rear microphone inlet port becomes the front microphone inlet port.
The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general-purpose signal processor or a block of random access memory, hard disk, or the like) or multiple pieces of hardware. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings. It should also be understood that the embodiments may be combined, or that other embodiments may be utilized, and that structural, logical and electrical changes may be made without departing from the scope of the various embodiments. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and their equivalents.
As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “an exemplary embodiment,” “various embodiments,” “certain embodiments,” “a representative embodiment,” and the like are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising”, “including”, or “having” an element or a plurality of elements having a particular property may include additional elements not having that property.
Furthermore, the term amplified listening device, as used herein, refers to hearing aids customized for specific users by manufacturers and hearing care professionals, personal sound amplification products, hearing protection devices, and any suitable devices that stream audio or amplify sounds with ambient noise features. Additionally, the term processor or processing unit, as used herein, refers to any type of processing unit that can carry out the required calculations, execute algorithms, and make data-driven decisions needed for the various embodiments, such as single or multi-core: CPU, Accelerated Processing Unit (APU), Graphic Processing Unit (GPU), DSP, FPGA, ASIC or a combination thereof.
Referring to
The first and second directional microphones 110a, 110b may be cardioid electret microphones (ccMICs) and/or any suitable microphones having a front microphone inlet port 112a, 112b and a rear microphone inlet port 114a, 114b. The directional microphones 110a, 110b tend to reject sound coming from the side and rear of the amplified listening device wearer. As such, the directivity of the directional microphones 110a, 110b may be used to improve the signal-to-noise ratio of the amplified listening device since it rejects a portion of the noise coming from the sides and behind the amplified listening device wearer. In a preferred embodiment, the second directional microphone 110b is turned around (i.e., reversed in space) behind the first directional microphone 110a such that the electrical output of the second directional microphone 110b is reversed in phase (i.e., opposite a phase of the first directional microphone 110a). Specifically, a positive pressure on the first directional microphone 110a is provided into the front microphone inlet port 112a as normal, while a positive pressure on the reversed second directional microphone 110b would go to the back of the second direction microphone diaphragm via the rear microphone inlet port 114b and produce an electrical signal having a reversed phase. The first electrical signal having a first phase is output from the first directional microphone 110a and a second electrical signal having a second phase opposite the first phase is output from the second directional microphone 110b. The first and second electrical signals output from the first and second directional microphones 110a, 110b, respectively, is provided to a resistive summing circuit 122 or low pass equalization circuitry 130a, 130b.
The first and second directional microphones 110a, 110b are arranged such that the front microphone inlet ports 112a, 112b and rear microphone inlet ports 114a, 114b are linearly aligned in a same plane. The rear microphone inlet port 114a of the first directional microphone 110a is positioned adjacent to the rear microphone inlet port 114b of the second directional microphone 110b because the second directional microphone 110b is turned around. Accordingly, from the position of the intended acoustic input (i.e., the front of the amplified listening device 100), the inlet ports 112a, 112b, 114a, 114b of the directional microphones 110a, 110b are arranged in an order of front microphone inlet port 112a of the first directional microphone 110a, rear microphone inlet port 114a of the first directional microphone 110a, rear microphone inlet port 114b of the second directional microphone 110b, and front microphone inlet port 112b of the second directional microphone 110b.
The first and second directional microphones 110a, 110b may be spaced apart approximately 6-8 millimeters (mm) in an in-the-ear (ITE) amplified listening device 100. The first and second directional microphones 110a, 110b may be spaced apart approximately 20 mm (e.g., 17-23 mm) in a behind-the-ear (BTE) amplified listening device 100. The front microphone inlet port 112a, 112b and rear microphone inlet port 114a, 114b of each of the first and second directional microphones 110a, 110b may be mounted approximately 4 mm (i.e., 3-5 mm) apart, so the free-space time delay for on-axis sound would be about 12 microseconds. In order to form a cardioid directional microphone, therefore, an internal time delay of 12 microseconds is provided by positioning an acoustic time-delay resistor 116a, 116b in the rear microphone inlet port 114a of the first directional microphone 110a and in the front microphone inlet port 112b of the second directional microphone 110b. The acoustic time-delay resistor 116a, 116b may be a mesh screen made of metal, plastic, fabric, and/or any suitable material. In this case, sound from the rear would experience the same time delays reaching a rear chamber of the first directional microphone 110a (or front chamber of the second directional microphone 110b) and a front chamber of the first directional microphone 110a (or rear chamber of the second directional microphone 110b), so that the net pressure across diaphragms of the first and second directional microphones 110a, 110b would be zero and a null in response would occur for 180 degrees sound incidence. Although the above example refers to embodiments implementing cardioid directional microphones 110a, 110b, any suitable directional microphone polar pattern may be implemented.
The resistive summing circuit 122 comprises resistors configured to add the first and second electrical signals output from the first and second directional microphones 110a, 110b to generate a second order directional response that may be output to low pass equalization circuitry 130, as shown in
In various embodiments, the resistive summing circuitry 122 may comprise two 22 kOhm resistors, for example, if the first and second directional microphones 110a, 110b have similar direct current (DC) voltages and sensitives. The resistive summing circuit 122 of the present technology does not include phase inverting circuitry. The two out-of-phase electrical signals output from the first and second directional microphones 110a, 110b as arranged according to embodiments of the present technology eliminates a need for the additional, expensive circuitry for performing electronic subtraction of two in-phase electrical signals. In an exemplary embodiment, the resistive summing circuit 122 may be provided on a circuit board 120 of the amplified listening device 100.
The low pass equalization circuitry 130 may comprise suitable logic, circuits, interface, and/or code configured to at least partially equalize the amplitude of the low frequency electrical signal components of the second order directional response with the amplitude of the mid and high frequency electrical signal components of the second order directional response. The equalized second order directional response may be provided to the amplifier 140, as shown in
The amplifier 140 may comprise suitable logic, circuits, interface, and/or code configured to process the equalized second order directional response signal to amplify the equalized second order directional response signal. In various embodiments, an amount of amplification provided by the amplifier 140 may be based on a volume control. The amplifier 140 outputs the amplified second order directional response electrical signal to the receiver 150. In an exemplary embodiment, the amplifier 140 may be provided on a circuit board 120 of the amplified listening device 100.
The receiver 150 may comprise suitable logic, circuits, interface, and/or code configured to convert the amplified second order directional response electrical signals to sound, which is communicated from the receiver 150 to a user's ear canal through an acoustic channel 174 in a sound tube 172.
Electronic components of the amplified listening device 100 may be implemented in software, hardware, firmware, and/or the like. The various electronic components of the amplified listening device 100 may be communicatively linked. Electronic components of the amplified listening device 100 may be implemented separately and/or integrated in various forms.
The battery 160 may be operable to provide power to directional microphones 110a, 110b, low pass equalization circuitry 130, 130a, 130b, amplifier 140, and/or receiver 150 in the amplified listening device 100. The battery 310 may be a cell, such as a 312 size zinc-air or lithium-ion cell, or any suitable battery or cell.
The housing 170, 180 may comprise a base 170 and cover 180 configured to house the directional microphones 110a, 110b, low pass equalization circuitry 130, 130a, 130b, amplifier 140, and receiver 150. The base 170 may comprise a sound tube 172 having an acoustic channel 174 for outputting sound from the receiver 150 to a user's ear canal. In various embodiments, the acoustic channel 174 of the sound tube 172 may comprise a damper 176 configured to smooth a frequency response. A volume control or toggle switch 182 may extend from the cover 180 of the housing 170, 180. The volume control or toggle switch 182 may be configured to adjust a volume of the amplified listening device 100 or switch between modes of the amplified listening device 100. For example, a volume control 182 may control the gain provided by the amplifier 140. As another example, a toggle switch 182 may be configured to switch between different operating modes of the amplified listening device 100, such as between a directional mode and an omnidirectional mode where the microphones are ccMICs that each include an omnidirectional microphone in addition to the directional microphone 110a, 110b.
The eartip 190 may be configured to attach to the sound tube 172 of the base 180 of the housing 170, 180. The eartip 190 may be configured to securely hold the amplified listening device 100 in a user's ear canal. For example, the eartip 190 may comprise three concentric circular flanges. The flanges can have increasing diameters, such that the flange furthest from the housing 170, 180 is the smallest, the flange closest to the housing 170, 180 is the largest, and the flange therebetween is an intermediate size. When inserted into a user's ear canal, the smallest flange enters first, and when fully inserted, the eartip can block exterior noise up to about 35 dB or more from entering the ear canal. Such eartips can come in other forms, such as a cylindrical foam eartip, a mushroom shaped foam eartip, or any suitable eartip.
At step 202, an acoustic input is received at a first directional microphone 110a to generate a first electrical signal having a first phase. For example, a first directional microphone 110a arranged normally with a front microphone inlet port 112a closest to the acoustic input (i.e., sound received from a front of amplified listening device 100) and a rear microphone inlet port 114a approximately 4 mm behind the front microphone inlet port 112a may receive the acoustic input. The rear microphone inlet port 114a comprises an acoustic time-delay resistor 116a that provides an internal time delay (e.g., approximately 12 microseconds). The acoustic time-delay resistor 116a may be a mesh screen made of metal, plastic, fabric, and/or any suitable material. The acoustic input is converted to a first electrical signal having a first (i.e., normal) phase by the first directional microphone 110a. The first electrical signal may be provided to a resistive summing circuit 122 or low pass equalization circuitry 130a.
At step 204, the acoustic input is received at a second directional microphone 110b to generate a second electrical signal having a second phase opposite the first phase. For example, a second directional microphone 110b arranged reversed in space (i.e., turned around) with a rear microphone inlet port 114b closest to the acoustic input (i.e., sound received from a front of amplified listening device 100) and a front microphone inlet port 112b approximately 4 mm behind the rear microphone inlet port 114b may receive the acoustic input. The front microphone inlet port 112b comprises an acoustic time-delay resistor 116b that provides an internal time delay (e.g., approximately 12 microseconds). The acoustic time-delay resistor 116b may be a mesh screen made of metal, plastic, fabric, and/or any suitable material. The rear microphone inlet port 114b and front microphone inlet port 112b of the second directional microphone 110b are linearly aligned in a same plane as the front microphone inlet port 112a and rear microphone inlet port 114a of the first directional microphone 110a. The acoustic input is converted to a second electrical signal having a second (i.e., reversed) phase by the second directional microphone 110b. The second phase is shifted 180 degrees from the first phase due to the reversed arrangement of the second directional microphone 110b. The second electrical signal may be provided to a resistive summing circuit 122 or low pass equalization circuitry 130b.
At step 206, the first and second electrical signals are combined with a resistive summing circuit 122 to generate a second order directional response. For example, the resistive summing circuit 122 comprises resistors configured to add the first and second electrical signals output from the first and second directional microphones 110a, 110b to generate a second order directional response that may be output to low pass equalization circuitry 130, as shown in
At step 208, the second order directional response is amplified to generate an output electrical signal. For example, an amplifier 140 may be configured to process the equalized second order directional response signal received from low pass equalization circuitry 130 (if the low pass equalization circuitry 130 is provided after the resistive summing circuit 122) or from the resistive summing circuit 122 (if the low pass equalization circuitry 130a, 130b is provided before the resistive summing circuit 122) to amplify the equalized second order directional response signal. The low pass equalization circuitry 130, 130a, 130b may comprise suitable logic, circuits, interface, and/or code configured to at least partially equalize the amplitude of the low frequency electrical signal components of the electrical signal received from the directional microphone 110a, 110b or resistive summing circuit 122 with the amplitude of the mid and high frequency electrical signal components of the electrical signal. The equalized second order directional response is provided to the amplifier 140, which processes the equalized second order directional response signal to amplify the signal. In various embodiments, an amount of amplification provided by the amplifier 140 may be based on a volume control. The amplifier 140 outputs the amplified second order directional response electrical signal to the receiver 150.
At step 210, the output electrical signal is transduced to an acoustic output. For example, a receiver 150 of the amplified listening device 100 may be configured to convert the amplified second order directional response electrical signals to sound. The sound may be communicated from the receiver 150 to a user's ear canal through an acoustic channel 174 in a sound tube 172.
Aspects of the present disclosure provide an amplified listening device 100 comprising two first-order directional microphones 110a, 110b arranged in tandem to form a second-order directional microphone system. The amplified listening device 100 may comprise a housing 170, 180 comprising a sound tube 172 having an acoustic channel 174. The amplified listening device 100 may comprise a first directional microphone 110a configured to provide a first electrical signal having a first phase. The first directional microphone 110a may comprise a first front microphone inlet port 112a closest a front of the amplified listening device 100. The first directional microphone 110a may comprise a first rear microphone inlet port 114a behind the first front microphone inlet port 112a. The amplified listening device 100 may comprise a second directional microphone 110b configured to provide a second electrical signal having a second phase opposite the first phase. The second directional microphone 110b may comprise a second rear microphone inlet port 114b adjacent the first rear microphone inlet port 114a of the first directional microphone 110a. The second directional microphone 110b may comprise a second front microphone inlet port 112b behind the second rear microphone inlet port 114b. The first front microphone inlet port 112a, the first rear microphone inlet port 114a, the second rear microphone inlet port 114b, and the second front microphone inlet port 112b are linearly aligned in a same plane. The amplified listening device 100 may comprise a resistive summing circuit 122 without phase inverting circuitry. The resistive summing circuit 122 may be configured to combine the first electrical signal and the second electrical signal to generate a second order directional response. The amplified listening device 100 may comprise a receiver 150 configured to convert the second order directional response to sound. The receiver 150 may be configured to output the sound through the acoustic channel 174 of the sound tube 172.
In an exemplary embodiment, the amplified listening device 100 may comprise a first acoustic time-delay resistor 116a in the first rear microphone inlet port 114a of the first directional microphone 110a. The amplified listening device 100 may comprise a second acoustic time-delay resistor 116b in the second front microphone inlet port 112b of the second directional microphone 110b. Each of the first acoustic time-delay resistor 116a and the second acoustic time-delay resistor 116b is configured to provide an internal time delay. In a representative embodiment, one or both of the first acoustic time-delay resistor 116a and the second acoustic time-delay resistor 116b is a mesh screen. In certain embodiments, the mesh screen comprises metal, plastic, or fabric. In various embodiments, the amplified listening device 100 comprises low pass equalization circuitry 130 configured to perform low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the second order directional response with a second amplitude of mid and high frequency electrical signal components of the second order directional response. In an exemplary embodiment, the low pass equalization circuitry 130 receives the second order directional response from the resistive summing circuit 122. The low pass amplification is performed prior to the receiver 150 converting the second order directional response to sound.
In a representative embodiment, the amplified listening device 100 comprises first low pass equalization circuitry 130a configured to perform low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the first electrical signal with a second amplitude of mid and high frequency electrical signal components of the first electrical signal. The amplified listening device 100 comprises second low pass equalization circuitry 130b configured to perform low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the second electrical signal with a second amplitude of mid and high frequency electrical signal components of the second electrical signal. In certain embodiments, the first low pass equalization circuitry 130a receives the first electrical signal from the first directional microphone 110a. The second low pass equalization circuitry 130b receives the second electrical signal from the second directional microphone 110b. The low pass amplification of the first electrical signal and the second electrical signal is performed prior to the resistive summing circuit 122 combining the first electrical signal and the second electrical signal to generate the second order directional response. In various embodiments, the amplified listening device 100 comprises an amplifier 140 configured to amplify the second order directional response signal prior to the receiver 150 converting the second order directional response to sound. In an exemplary embodiment, one or both of the first directional microphone 110a and the second directional microphone 110b is a cardioid electret microphone (ccMIC).
Various embodiments provide a method 200 for providing a second order acoustic output via two first-order directional microphones 110a, 110b arranged in tandem to form a second-order directional microphone system of an amplified listening device 100. In accordance with various embodiments, the method 200 may comprise receiving 202 an acoustic input at a first directional microphone 110a of an amplified listening device 100. The first directional microphone 110a comprises a first front microphone inlet port 112a closest a front of the amplified listening device 100. The first directional microphone 110a comprises a first rear microphone inlet port 114a behind the first front microphone inlet port 112a. The method 200 may comprise generating 202, by the first directional microphone 110a, a first electrical signal having a first phase. The method 200 may comprise receiving 204 the acoustic input at a second directional microphone 110b of the amplified listening device 100. The second directional microphone 110b comprises a second rear microphone inlet port 114b adjacent the first rear microphone inlet port 114a of the first directional microphone 110a. The second directional microphone 110b comprises a second front microphone inlet port 112b behind the second rear microphone inlet port 114b. The first front microphone inlet port 112a, the first rear microphone inlet port 114a, the second rear microphone inlet port 114b, and the second front microphone inlet port 112b are linearly aligned in a same plane. The method 200 may comprise generating 204, by the second directional microphone 110b, a second electrical signal having a second phase opposite the first phase. The method 200 may comprise combining 206, by a resistive summing circuit 122 of the amplified listening device 100, the first electrical signal and the second electrical signal to generate a second order directional response. The resistive summing circuit 122 does not include phase inverting circuitry. The method 200 may comprise converting 210, by a receiver 150 of the amplified listening device 100, the second order directional response to sound. The method 200 may comprise outputting 210, by the receiver 150, the sound through an acoustic channel 174 of a sound tube 172 of the amplified listening device 100.
In certain embodiments, a first acoustic time-delay resistor 116a is positioned in the first rear microphone inlet port 114a of the first directional microphone 110a. A second acoustic time-delay resistor 116b is positioned in the second front microphone inlet port 112b of the second directional microphone 110b. Each of the first acoustic time-delay resistor 116a and the second acoustic time-delay resistor 116b provides an internal time delay. In various embodiments, one or both of the first acoustic time-delay resistor 116a and the second acoustic time-delay resistor 116b is a mesh screen. In an exemplary embodiment, the mesh screen comprises metal, plastic, or fabric. In a representative embodiment, the method 200 comprises performing 208, by low pass equalization circuitry 130 of the amplified listening device 100, low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the second order directional response with a second amplitude of mid and high frequency electrical signal components of the second order directional response. In certain embodiments, the method 200 comprises receiving 206, 208, by the low pass equalization circuitry 130, the second order directional response from the resistive summing circuit 122. The low pass amplification 208 is performed prior to the converting 210 the second order directional response to sound.
In various embodiments, the method 200 comprises performing 202, 206, 208, by first low pass equalization circuitry 130a, low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the first electrical signal with a second amplitude of mid and high frequency electrical signal components of the first electrical signal. The method 200 may comprise performing 204, 206, 208, by second low pass equalization circuitry 130b, low pass amplification by at least partially equalizing a first amplitude of low frequency electrical signal components of the second electrical signal with a second amplitude of mid and high frequency electrical signal components of the second electrical signal. In an exemplary embodiment, the method 200 comprises receiving 202, 206, 208, by the first low pass equalization circuitry 130a, the first electrical signal from the first directional microphone 110a. The method 200 may comprise receiving 204, 206, 208, by the second low pass equalization circuitry 130b, the second electrical signal from the second directional microphone 110b. The low pass amplification 202-208 of the first electrical signal and the second electrical signal is performed prior to the combining 206 the first electrical signal and the second electrical signal to generate the second order directional response. In a representative embodiment, the method 200 comprises amplifying 208, by an amplifier 140 of the amplified listening device 100, the second order directional response signal prior to the converting 210 the second order directional response to sound. In certain embodiments, one or both of the first directional microphone 110a and the second directional microphone 110b is a cardioid electret microphone (ccMIC).
As utilized herein the term “circuitry” refers to physical electronic components (i.e. hardware) and any software and/or firmware (“code”) which may configure the hardware, be executed by the hardware, and or otherwise be associated with the hardware. As used herein, for example, a particular processor and memory may comprise a first “circuit” when executing a first one or more lines of code and may comprise a second “circuit” when executing a second one or more lines of code. As utilized herein, “and/or” means any one or more of the items in the list joined by “and/or”. As an example, “x and/or y” means any element of the three-element set {(x), (y), (x, y)}. As another example, “x, y, and/or z” means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms “e.g.,” and “for example” set off lists of one or more non-limiting examples, instances, or illustrations. As utilized herein, circuitry is “operable” and/or “configured” to perform a function whenever the circuitry comprises the necessary hardware and code (if any is necessary) to perform the function, regardless of whether performance of the function is disabled, or not enabled, by some user-configurable setting.
The present disclosure may be realized in hardware, software, or a combination of hardware and software.
While the present disclosure has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed, but that the present disclosure will include all embodiments falling within the scope of the appended claims.
The present application claims priority under 35 U.S.C. § 119(e) to provisional application Ser. No. 63/183,746 filed on May 4, 2021, entitled “SYSTEM AND METHOD FOR PROVIDING AN ARRANGEMENT OF TWO FIRST-ORDER DIRECTIONAL MICROPHONES ARRANGED IN TANDEM TO FORM A SECOND-ORDER DIRECTIONAL MICROPHONE SYSTEM.” The above referenced provisional application is hereby incorporated herein by reference in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 7832080 | Killion | Nov 2010 | B2 |
| 20080273727 | Hagen | Nov 2008 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20220360916 A1 | Nov 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| 63183746 | May 2021 | US |
